Until now, hip prostheses have included a cotyloidal element positioned in the cotyloidal cavity of the pelvis; and fixing of the element to the pelvis bone being ensured both using cement of the methyl methacrylate type, and making use of irregularity of the surface in contact with the bone, the irregularity being brought about using a range of processes (small cuts, pitting, scores and so on). The disadvantage of these processes lies in the fact that neither methyl methacrylate nor the materials used to obtain a bond in the pelvic cavity has the same Young's modulus (elastic modulus) as the spongy tissue of the pelvis. The principle of selffixing of the present invention is based on the proximity of the Young's modulus of the prosthesis to that of the spongy tissue of the pelvis, making it possible to have two materials next to each other which are compatible.
The same problem arises with regard to the femoral prosthesis where attachment of the prosthesis in the medullary canal of the bone is provided using either, as was the case for the pelvis, methyl methacrylate which compensates for the lack of match between the tail of the femoral prosthesis and the diameter of the medullar cavity, or by using a metal prosthesis with a larger diameter and having, as was the case for the pelvis, irregularities intended for correct fixing of the bone onto these irregularities.
Here, too, the difference in the Young's modulus which exists between steel and methyl methacrylate on the one hand, and the cortical bone of the femur on the other, is such that under the effect of mechanical stresses, loosening occurs leading to the need for further complete surgical work.
The femoral prosthesis concerned in this invention is intended to be fixed not in the medullar cavity but in the spongy tissue of the femoral head and neck, by using a material of which the Young's modulus is close to that of the spongy tissue (high density polyethylene).
Two small tongues in polyethylene are introduced into the spongy tissue and, owing to their elasticity, become engaged with this spongy tissue so that an osseous growth is able to form around these tongues in polyethylene and provides longterm attachment of the prosthetic elements.
At the pelvis end, additional attachment is provided using clips so that a dynamic connection is made between the cotyloidal element and the cavity which receives it.
The description which follows, with reference to the attached drawings, given only by way of example, will fully explain how the invention may be carried out.